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Chemistry
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Hydrofluoric acid is a weak monoprotic acid with Ka = 6.6×10-4 M. 

1)Calculate the pH of a 6.99×10-2 M solution of hydrofluoric acid. 

2)Calculate the pH of a solution that contains 6.99×10-2 M hydrofluoric acid and 5.59×10-2 M sodium fluoride.

Feb 16th, 2015

1)

HF     =>     H+       +       F-     ; Ka=6.6*10^-4

(6.6*10^-4) = (x^2) / (0.0699 - x)      [rearrange and quadratic formula]

=> x = 6.5 * 10^-3 M = [H+]

so pH = -log(6.5 * 10^-3) = 2.19

2)

pH = pKa + log[base]/[acid]

pH = -log(6.6*10^-4) + log[(0.0559)/(0.0699)] = 3.08

Feb 16th, 2015

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Feb 16th, 2015
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Feb 16th, 2015
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